The present invention relates to a method of and an arrangement for establishing underground passages in general, and more particularly to establishing underground passages which are either horizontal or have a predetermined slope along their course.
There are already known various methods of establishing underground passages, including those for establishing lined tunnels, underground channels, adits or drifts, and so on. Many of these methods and many arrangements for performing such methods are rather complex and laborious. There is, however, already known a relatively simple method of establishing such underground passages, which resides in advancing a line of consecutive pipe sections through the ground, provided that the latter is sufficiently yieldable to permit penetration of the line of pipe sections therethrough. The present invention is primarily concerned with underground passages which have been established in this advancing process.
As already mentioned above, this conventional advancing process of establishing undergound passages is rather simple and the necessary equipment for performing such a process also has a very low degree of complexity. However, experience with this advancing process has shown that it is possessed of one rather serious drawback when used in connection with establishing, for instance, underground draining passages or the like. More particularly, such passages are, more often than not, to be established in regions where the earth surface is flat or has only a minute inclination with respect to the horizontal. Under these circumstances, it is necessary to give the underground passage a quite minute slope in order to assure natural flow of water or similar liquid therethrough. Such inclination amounts, for instance, to 6 centimeters per 100 meters of length of the underground passage or channel. It will be appreciated that close adherence to this inclination in all regions of the underground passage is imperative especially under these circumstances.
When the underground passage is established in the advancing process which has been mentioned previously, it will often happen that the leading end of the line of consecutive pipe sections which is being advanced through the ground meets some obstructions as it is being advanced along the desired course of the passage, such as rocks, boulders and the like. When encountering such obstructions, first the leading end of the line of consecutive pipe sections and subsequently the line in its entirety will be easily deflected from the desired course and will continue its advancement in a path which is offset from the desired course at least in the immediate vicinity of the obstruction. However, inasmuch as it is very difficult if not impossible to immediately detect the deviation of the leading end of the line of pipe sections from the desired course and to take immediate corrective measures, a situation arises in which, for instance, a boulder which extends to the extent of several centimeters into the desired course causes a deviation from the desired course of the advancing line of consecutive pipe sections which amounts to several decimeters, inasmuch as the leading end of the line of consecutive pipe sections or a cutting arrangement provided thereon, and the following consecutive sections, due to their inflexibility, have to gradually glide over the above-mentioned boulder and can be deflected toward the original desired course only after passing the boulder or other obstruction. This is true even when the deflection of the leading end of the line of consecutive pipe sections is detected immediately and the corrective measures are attended to at the first opportunity. The situation is even worse when the deviation of the path of advancement of the consecutive pipe sections from the desired course is detected only after a certain period of time has elapsed subsequent to the encounter with the obstruction.
When such a deviation of the advancement path from the desired course occurs in a horizontal plane, it can be often accepted inasmuch as it may be of no consequence that the underground passage is slightly curved in the horizontal plane. However, when such a deviation occurs only or also in a vertical plane this may have very serious consequences, particularly in the above-mentioned circumstances where it is imperative that the desired inclination or slope of the underground passage be maintained. The existence of even one substantial deviation from the desired course in the vertical direction, which may be the result of a quite insubstantial projection of an obstruction into the desired course, anywhere along the passage which may be quite long, may render the entire passage useless inasmuch as the water or a similar fluid will tend to accumulate upstream of the location of the deviation, such deviation, in effect, resulting in the formation of a dam which may prevent the passage of the water or similar fluid through the passage altogether. Inasmuch as such deviations cannot be avoided during the advancing process in ground or soil which may contain scattered obstructions, it was heretofore necessary to abandon the underground passage which included such a deviation from the desired course, and to establish another underground passage next to the abandoned passage. This approach, however, is very expensive, particularly in terms of manhours, results in unnecessary wear of the machinery which is used for performing the advancing process, and sometimes cannot be used at all, particularly in crowded conditions where there is simply no space available for establishing the additional, hopefully correct, underground passage.